RFI Mitigation at Westerbork: algorithms, test observations, system implementation Willem Baan, Peter Fridman & Rob Millenaar

Implementing Mitigation Hardware in the WSRT system 3 locations in data flow of system 3 locations in data flow of system different algorithms at different stages different algorithms at different stages stapling of methods stapling of methods AI decision-making subsystem for control AI decision-making subsystem for control

Our first DSP system

WSRT RFIMS WSRT RFIMS Main goal RFIMS is to recover (full) sensitivity of WSRT across all observing bands with hostile RFI environmentMain goal RFIMS is to recover (full) sensitivity of WSRT across all observing bands with hostile RFI environment Three year implementation planThree year implementation plan System scalability and upgradeabilitySystem scalability and upgradeability RFIMS pre-processing 14 x 2 x 20 MHz FPGA hardwareRFIMS pre-processing 14 x 2 x 20 MHz FPGA hardware Possible implementation of 10msec sampling at WSRT correlator for on-line processingPossible implementation of 10msec sampling at WSRT correlator for on-line processing Envisioned implementation on other telescopesEnvisioned implementation on other telescopes

WSRT RFI Mitigation System Real-time pre-detection and pre- correlation baseband processing a) 12bit ADC b) Altera Stratix FPGA c) 14bit DAC d) VME control e) 40Msamples/sec 14 RTs & 2pol & 20 MHz & 20 MHz

RFIMS

Processor Board Layout

A fancy processor

RFI time-frequency domains

Thresholding in Time Domain

Thresholding in Frequency Domain Reference power spectrum Median Filtering of spectrum

Adaptive Filtering with WSRT

2004 Adaptive Filtering - Proposed

Adaptive Filtering - Ultimate

Dual Channel FPGA Layout

FPGA layout with Reference antennas

T-f thresholding First trial of 14 RT system 20 MHz 5X band cleaned All other 7 bands at same frequency 10 hr synthesis of DA240

Auto Corr Amp 5X5X b0 & b1 RT 5X, 6X, 7X, 9X

Cross Corr Amp 5X6X b0 & b1

Cross Corr Func 5X6X b0 & b1

RFIMS 4X & 5X

DA240 field

Short Term Plans Persuade astronomers to use the system Use RFIMS with new 14 RT LFFE system in LOFAR band MHz Implement adjacent RT for reference antenna Introduce separate Refants Apply ANC for pulsar operations (PuMa I & II) Implement HOS for blanking Evaluate efficiency and impact on the imaging and spectrum data

1. Single dishes and connected radio interferometer 2. Evaluate algortihms for RFI environments 3. Implement in ALL new RTs ( multi-bit ADC (>14)), short averaging intervals, higher order statistics, auxiliary reference channels). 4. Number crunching aspects 5. Dedicated devices ? Conclusions